It is proposed to conduct a detailed investigation on the chemical structures of seven serotype antigens of Pseudomonas aeruginosa. These antigens are all complex lipopolysaccharides which are markedly effective, in combination , as a vaccine for immunizing human subjects against Pseudomonas infections that are a major cause of death in patients who have been severely burned. Comparative structural studies on the seven serotype antigens now available may greatly assist in the rapid classification of Pseudomonas strains isolated from hospital subjects, may help in devising chemical modifications of the vaccine to eliminate undesirable side-effects following parenteral administration, and a correlation between chemical structure and interferon- stimulating activity of the antigens may provide knowledge useful in the understanding of cancer and viral diseases. The structural studies will be conducted by specific degradative methods to characterize the component fragments of each lipopolysaccharide antigen and to determine their mode of linkage in the parent molecule, by use of gas-liquid chromatography-mass spectrometry and other techniques in a well equipped laboratory experienced in structural studies on complex carbohydrate derivatives.